Using the minimum spanning tree to trace mass segregation

TL;DR

This paper introduces a new MST-based method to detect and quantify mass segregation in star clusters, successfully applied to simulated data and the Orion Nebula Cluster, revealing varying levels of segregation among different stellar mass ranges.

Contribution

The paper presents a novel MST-based technique for measuring mass segregation, validated on simulations and applied to real star cluster data, providing a new quantitative tool.

Findings

The method detects strong mass segregation in the Trapezium down to 16 solar masses.

It finds lower but significant segregation in the ONC down to 5 solar masses.

No further mass segregation is observed below 5 solar masses.

Abstract

We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that of random stars. If mass segregation is present, the MST length of the most massive stars will be shorter than that of random stars. This difference can be quantified (with an associated significance) to measure the degree of mass segregation. We test the method on simulated clusters in both 2D and 3D and show that the method works as expected. We apply the method to the Orion Nebula Cluster (ONC) and show that the method is able to detect the mass segregation in the Trapezium with a `mass segregation ratio' \Lambda_{MSR}=8.0 \pm 3.5 (where \Lambda_{MSR}=1 is no mass segregation) down to 16 \Msun, and also that the ONC is mass segregated at a lower level (~2.0 \pm 0.5) down to 5 \Msun. Below 5 \Msun we find no evidence for any further mass segregation in the ONC.